1. Field of the invention:
This invention relates to a semiconductor laser device which oscillates to develop high output power laser lights with a 0.degree.-phase shift therebetween and more particularly to the optical waveguide producing semiconductor element utilized therein.
2. Description of the prior art:
Semiconductor laser devices having a single lasing filament structure can only produce about 50 mW of light energy at their best. In order to produce high output power, semiconductor laser devices have been studied, in which a plurality of lasing filaments are disposed in a parallel manner on the same substrate to achieve an optical phase coupling between the adjacent lasing filaments.
Provided that two lasing filaments are parallelly disposed on the same substrate, there will be three relationships between the laser oscillation of adjacent filaments: The first is that the two laser lights obtain attain a 0.degree.-phase shift therebetween, the second is that the optical phase shift between the two laser lights is 180.degree.. And the third is a mixture of the above-mentioned cases. A far-field pattern in the first case, as shown in FIG. 3(A), has a single peak so that the two laser lights can be concentrated into a spot by means of optical lenses. However, far-field patterns in the second and third cases, as shown in FIGS. 3(B) and 3(C), respectively, have plural peaks so that the two laser lights cannot be concentrated onto a single spot by any optical lens. Thus, semiconductor laser array devices, including gain-guided semiconductor laser array devices and index-guided semiconductor laser array devices in which a plurality of lasing filaments are disposed in a parallel manner to achieve an optical phase coupling between the adjacent filaments, have been proposed.
However, in gain-guided semiconductor laser array devices, the electric field in the center area between the adjacent lasing filaments is zero, so that the laser lights must be produced with a 180.degree.-phase shift therebetween, resulting in a far-field pattern having plural peaks. On the other hand, in index-guided semiconductor laser array devices, the electric field between the adjacent lasing filaments is not necessarily zero, so that laser lights with a 0.degree.-phase shift therebetween is not always attained. It can be said that semiconductor laser array devices attaining a 0.degree.-phase shift between the adjacent filaments cannot be easily fabricated by the simple disposition of plural lasing filaments in a parallel manner.